Jet and anvil comminuting apparatus, and method

ABSTRACT

Dry grinding of the jet and anvil type is improved by removing partially ground material from the grinding chamber and then reinjecting it into the chamber against a plurality of rotating anvils. The grinding procedure is further enhanced by removing a portion of the gas carrying the material so as to reduce the load which must be accelerated by the jet.

United States Patent Andrews [4 1 Sept. 5, 1972 [54] JET AND A NVIL COMMINUTING APPARATUS, AND METHOD [72] Inventor: Norwood H. Andrews, PO. Box 68,

4 Moorestown, NJ. 08057 [22] Filed: July 30, 1970 [21] Appl. No.: 59,387

[52] US. Cl. ..24l/5, 241/27, 241/39, I 241/67 [51] Int. Cl ..B02c 19/06 [58] Field of Search ..24l/5, 27, 39, 40, 41, 47, 241/67 [56] References Cited UNITED STATES PATENTS 2,590,220 3/1952 Stephanofi ..241/5 X 2,448,049 8/ 1948 Rafton ..24l/5 X 3,093,327 6/1963 Harvey et al .,24l/47 X 3,398,900 8/1968 Guba et a]. ..24l/67 3,348,779 10/ l 967 Andrews, ..241/39 I Primary Examiner-Granville Y. Custer, Jr. 9

Attorney-Seidel, Gonda &. Goldhammer ABSTRACT Dry grinding of the jet and anvil type is improved by removing partially ground material from the grinding chamber and then re-injecting 'it into the chamber against a plurality of rotating anvils. The grinding procedure is further enhanced by removing a portion of the gas carrying the material so as to reduce the load which must be accelerated by the jet.

17 Claims, 13 Drawing Figures PATENTEDSEP m 3.688.991

SHEET 2 0F 5 F/6.4 w l2 W IN VEN 70/? NOR W0 00 H. A NDRE ws ATTORNEYS PATENTEI'JsEP- 5:912

SHEET 3 [If 5 INVENTOR NORWOOD H. ANDREWS ATTORNEYS PHENTEDSEP 5 19 2 SHEET 0 BF 5 2 w, 6/7 W \Q R 0 w E V w I NORWOOD H. ANDREWS /66 A TTORNE rs PmmEnsn's-mz I 3.688.991 SHEEI S [If 5 INVENTOR NORWOOD H. ANDREWS ATTORNEYS JET AND ANVIL COMMINUTING APPARATUS, AND METIIOD This invention relates to an apparatus and method for performing jet and anvil grinding. More particularly, this invention relates to an apparatus and method for improving the grinding of materials using jet net and anvil.

There are several known types of apparatus for grinding particles into small sizes. Among these are the hammer or ball mill, jet mill, and the jet and anvil mill. Each of these mills has certain advantages for grinding particular types of materials. For example, jet grinding is advantageously used in the low micron range for dry grinding as compared to a ball mill. A ball mill produces a much finer product when wet grinding than when dry grinding. In the case of a ball mill, the material and balls are surrounded by an air film when the material approaches the extremely fine, dry state. Material is squeezed out from between the balls and therefore eludes further grinding. Stated otherwise,'the air film seems to work as a cushion to protect the material from further comminution. On the other hand, the ball mill is extremely effective in wet milling due to the greater viscosity of the medium. This prevents the fine particles from escaping as the balls come together. Consequently a finer product is obtained. In other words, it is necessary to insure that fine particles are so constrained that they can be acted on vby any means. For dry grinding, the jet mill is more effective in the low micron range because even the finest particles of material can be readily aspirated into jet streams for impact with each other. See, for example, U.S. Pat. Nos. 2,032,827 and 2,219,011. In U.S. Pat. Nos. 1,935,344 and 2,735,726 the materials are aspirated into opposing jet streams to provide the particle to particle impacting force.

Another form of jet grinding is the so-called jet and anvil wherein the material is aspirated into a jet and thereafter projected against an anvil. Examples of the jet and anvil type of apparatus are illustrated in U.S. Pat. Nos. 1,847,009 and 2,487,088. Another form of anvil grinding is described in U.S. Pat. Nos. 2,392,019 and 3,184,169 where the material is not aspirated into the jets. Instead, it is introduced directly into the high pressure gas and projected through a nozzle or orifice into impact with an anvil, or into impact with material projected in the same manner from the opposite direction.

All of the apparatus described in the foregoing patents is more or less effective, depending upon the type of material to be ground. The jet and anvil type of apparatus is particularly effective because the jets are capable of imparting an extremely high velocity to the particles to be ground. This is true whether the material is aspirated into the jet stream or introduced directly into the high pressure line. Even here, however, there are lower limits on the size of particle that can be produced. It has been known for many years that the material under reduction is considerably decelerated before it impacts against the anvil. This is due to the fact that the high velocity gas carrying the material also impacts against the anvil. As a result, a pressure head extending outwardly in all directions from the face of the anvil is created. This head must be penetrated by the material before it impacts against the anvil. As a result, the particles are decelerated since a certain amount of their force must be used up in-penetrating the head. To overcome the pressure head, which is greatest when the anvil is closest to the discharge end of the accelerating means, many shapes of anvils, both concave and convex have been designed with varying success. See, for example, the curvilinear anvil illustrated on the front cover of Chemical Processing, Volume 29, No. 7, July 1966. Another approach has been to position the anvil at a considerable distance from thedischarge end of the accelerating jet so that the material carrying gas is free to expand conically outward from the axis of the jet. On reaching the anvil, the gas covers a'much larger area. This results in a considerable reduction in the amount of pressure in the head.

All of the foregoing has been somewhat effective in grinding coarser materials where the surface area is small in respect to the weight of the individual particles. But when grinding to low micron sizes, the surface area of the individual particles necessarily becomes increasingly large with respect to its weight. As a result, the particles are increasingly slowed down in their penetration of the pressure head regardless of the shape used. Where the approach has been to position the anvil at a further distance form the nozzle, the smaller particles tend to follow the gas as it spreads outwardly. In either case, the velocity of impact with the anvil is greatly reduced as the particles become finer.

The present invention is directed to an improvement in the jet and anvil type of grinder. In particular, the present invention is directed to a device which substantially removes the decelerating means while at the same time creating a new impact force in such a manner that the total effect is to produce dry grinding in a range heretofore unattainable in a jet and anvil comminuting apparatus. In particular, the present invention provides a new jet and anvil type of grinding apparatus which permits the anvil to be as close as possible to the jet, while at the same time substantially removing the pressure head effect heretofore described.

In accordance with the present invention, the grinding of materials by the jet and anvil method is greatly enhanced, particularly in the low micron region, by projecting the materials by means of a jet against a series of rotating anvils. By rotating the anvils, a new anvil is presented to the jet and the material contained in the gas exiting from it in rapid succession. As a result,- the pressure head has little opportunity to build up. Moreover, the anvils can be-brought into close proximity with the jet thereby eliminating the conical carry off effect when the particles reach the low micron range.

As previously stated, the. present invention is particularly effective in grinding materials in the low micron range. For this reason, this invention incorporates the concept of impacting partly ground materials against the rotating anvils, rather than the raw material itself. However, it is contemplated that in certain instances raw material may be added directly to the partly ground material for impact against the rotating anvils.

In accordance with the present invention, material to be ground to fine micron size is discharged from the grinding chamber and then re-injected by an acceleration means such as a high speed jet into opposed impact with a series of anvils crossing the path of the re-injection jet at a rate of several hundred anvils per second.

In still another aspect of the present invention it has been found that the particle sizes can be greatly reduced by separating the particle carrying gas from the material itself prior to re-injection into the apparatus. It has been found that the gas itself forms part of the load which must be accelerated by the re-injection means, such as the jet. Since this gas performs no function other than to carry the partially ground material, it is advantageous to reduce it to a minimum and either use it for other purposes, such as to classify, or remove it altogether.

Still another aspect of the present invention is to provide an apparatus for performing the method as well as to combine such apparatus with other known grinding apparatus. Thus, the apparatus may be combined with a jet grinding apparatus or a toroidal mill, such as is well known in the art.

Still another aspect of the present invention is to provide a new and improved driving shaft for the apparatus described herein. This is especially designed to be used when superheated steam or other hot gases are the grinding medium.

These and other objects of the invention will become apparent from what follows.

For the purpose of illustrating the invention, there are shown in the drawings forms which are presently preferred; it being understood, however, that this invention is not limited to the precise arrangements and instrumentalities shown.

FIG. 1 is a partial longitudinal sectional view of a jet and anvil comminuting apparatus constructed in accordance with the present invention.

FIG. 2'is a transverse sectional view of the apparatus illustrated in FIG. 1 taken along the line 2-2.

FIG. 3 is a transverse sectional view of the apparatus illustrated in FIG. 1 taken along the line 33.

FIG. 4 is a longitudinal sectional view of a water cooled hollow drive shaft for the apparatus taken along the line 4-4 in FIG. 3.

FIG. 5 is a partial sectional view of a jet and anvil comminuting apparatus forming a second embodiment of the present invention.

FIG. 6 is a transverse sectional view of the apparatus illustrated in FIG. 5 taken along the line 6-6.

FIG. 7 is a sectional view ofa jet and anvil comminuting apparatus defining yet another embodiment of the present invention.

FIG. 8 is a sectional view of the apparatus illustrated in FIG. 7 taken along the line 8-8.

FIG. 9 is a sectional view of still another embodiment of the present invention.

FIG. 10 is yet another embodiment of an apparatus constructed in accordance with the present invention.

FIG. 11 is a partial sectional view of the apparatus illustrated in FIG. 10 taken along the line 1 1-1 1.

FIG. 12 is' still another embodiment of an apparatus constructed in accordance with the present invention.

FIG. 13 is a partial sectional view of the apparatus illustrated in FIG. 12 taken along the line 13-13.

Referring now to the drawings in detail, wherein like numerals indicate like elements, there is shown in FIGS. 1, 2, 3, and 4, a comminuting apparatus designated generally as 10 and constructed in accordance with the principles of the present invention. As shown, the apparatus includes an endless chamber 12 which in this invention takes the form of a cylindrical chamber. The chamber 12 is provided with a product outlet 14, towards which particles of small enough micron size are carried by a vortical stream of gas in the manner well known in the art. Mounted on the shaft 16, soon to be described, is a frame 18 which supports at its outer periphery a plurality of anvils 20. The frame 18 and anvils 20 are rotatably driven by the shaft 16 which is turned by the pulley 22 driven bythe belt 24. As best shown in FIG. 3, the pulley 22 is keyed to the shaft 16 by the key and slot 26. The pulley 24 is chamber 12 by the feed assembly 29 which includes the funnel 30, nozzle 32 and venturi 34. A supply of high pressure gas (not shown) is connected to the nozzle 32. Thus, the gas discharged by the nozzle aspirates the raw material from the funnel 30 into the venturi 34 where it is accelerated into the interior of chamber 12. The

material is directed into the interior of chamber 12 so that it impacts against the radially extending portions 36 of the anvils 20. This same concept is illustrated in FIG. 11 of U.S. Pat. No. 3,348,779. The impaction of the radial portion 36 of the anvil 20 against the raw material serves to partially comminute it. The material thereafter is carried by a gaseous stream along the wall 28 until it is exhausted through the discharge tube 38. The centrifugal force of the gas and partially ground material cause it to enter the discharge tube which, as shown, is tangentially positioned in the wall 28 of the chamber 12.

The discharge tube 38 is directly connected to the acceleration means 39, which includes the nozzle and the axially aligned venturi 42, as shown in FIG. 2.

' The nozzle 40 is connected to a source of high pressure gas so that the partially ground material and gas is aspirated into the stream and directed through the venturi 42 which accelerates the same. The venturi 42 directly communicates through an opening in the wall 28 with the interior of the chamber 12. The venturi is aligned so that the gas and material emitting from its discharge end are re-injected back into the chamber 12 against the surfaces of the rotating anvils 20. As shown in FIG. 2, the anvils are rotating in a clockwise direction, but the venturi 42 is directed substantially in the opposite tangential direction. Thus, the material carried by the gas is re-injected normal to and against the rotating anvils.

In operation, the frame 18 may be rotated at any chosen speed to produce the particular result, depending upon the type of material to be ground. However, the basic principle calls for the presentation of successive anvils to the exit port of the venturi against which material is impacted. By presenting a fresh anvil in rapid succession to the re-injected material, the pressure head is practically eliminated. Moreover, the anvil is effectively positioned extremely close to the venturi as it passes across the end of the accelerating means 39.

In operating a device of the type described, it has been found that it provides much improved results over a wide range of product sizes. However, it has proved to be most effective in the low micron size range. Improvements have been found to exist not only in the improved size reduction, but also in the amount of power and time required to achieve such size reductions.

Referring now to FIG. 4, the water-cooled, hollow shaft 16 for driving the frame 18, and hence the anvils 20 is illustrated in detail. Shaft 16 is rotatably mounted by bearings 40 and 42 which are fixed to bearing mounts 44 and 46, respectively. The frame 18 is mounted to the shaft 16 on a reduced diameter portion thereof 48 which provides a shoulder against which the frame 18 may be abutted. The frame is fixed in nonrotative position on the shaft 16 by an appropriate key and slot 50. The frame 18 is fixed to the shaft by a flanged clamping bolt 52 which threadedly engages the inside wall of the shaft.

The shaft 16 extends through an opening 54 in the wall of chamber 12. To prevent gas escaping along the shaft 16, it is sealed by a stuffing box designated generally as 56. The stuffing box 56 includes a housing 58 that is bolted by means of flanges 60 and threaded fasteners 62 to the wall of chamber 12. Mounted within the stuffing box 58 and abutting the wall of chamber 12 is a first annular ring 64 which is provided with inner and outer circumferential grooves 66 and 68. Groove 66 defines a closed channel together with the housing 58. Groove 68 with its close clearance defines'with the shaft 16 substantially an inner closed channel. Grooves 66 and 68 are interconnected by a series of ports 70 extending radially through the ring 64. The groove 66, as shown, is connected to a source of air through the port 74 in the housing 58. The purpose of the described structure is to maintain a moderate flow of air into the mill through the opening 54. This prevents any dust from working itself back into the stuffing box and destroying the packing. v

The stuffing box 58 is provided with a plurality of conventional, heat-resistant packings 76 which are sealed into the box by means of a threaded gland 78.

The amount of gas passing through opening 54 depends upon the clearance between housing wall 12 and the shaft 16. Obviously, the closer the fit, the less gas required to maintain a slight flow from the inner channel along the clearance 54 between the shaft and chamber 12. The rate of flow is (for any required pressure differential between channel 68 and chamber 12) proportional to the area of the circumferential clearance between the shaft and chamber wall 12.

As previously indicated, the hollow shaft 16 and stuffing box 56 are water-cooled. Cooling water is supplied through the pipe 80 connected to a source of water coolant (not shown). Pipe 80 extends into the hollow shaft 16 almost up to the inner end of flanged bolt 52. It is held concentrically within the shaft 16 by means of a plate 82 having an L-shaped flange 84 which surrounds the shaft 16. The flange 84 is sealed to the shaft 16 by means of an O-ring 86. The flange 82 is held in position at the end of shaft 16 by a bracket 88 fixed by means of threaded fastener 90 to the bearing mount 44 or some other fixed object. The pipe 80 is held in an opening in plate 82 by means of a set screw 92.

The plate 82 is also provided with an outlet pipe 94 for discharging the cooling water.

Cooling water flows through the pipe past the wall of chamber 12 and up against the flanged bolt 52, where it reverses the direction of flow and then moves back over the inner surfaces of the hollow shaft 16. The water cools the packing within the stuffing box 56 as well as the bearings 42 and 40.

The cooling means illustrated in FIG. 4 has particular utility for large mills which use superheated steam (usually from 700F to over 1.,000F). At such temperatures it is necessary ot protect the stuffing in the stuffing box as well as the bearings in a reliable manner. When the mill uses relatively cool compressed gases, various types of conventional sealing means can be used in place of the apparatus illustrated in FIG. 4. However, regardless of the type of gas, it is necessary to prevent finely ground material from flowing along the shaft from the mill to the sealing means.

Referring now to FIGS. 5 and 6, there is shown a second embodiment of the present invention wherein the apparatus illustrated in FIG. 1 is improved 'to more efficiently comminute particles down to extremely fine particle size, as well as to grind to a smaller size than heretofore possible with jet and anvil type apparatus.

The apparatus illustrated in FIGS. 5 and 6 is similar to that illustrated in FIG. 1 in that it includes an endless chamber 12' having a central product outlet 14 for permitting particles of the appropriate size to be carried out from the chamber 12' in accordance with the principles well known in the art. A plurality of anvils 20' are mounted on a frame 18 which in turn is fixed to shaft 16 within the chamber 12'. Shaft '16 is driven by means such as those illustrated in FIG. 4. Accordingly, the details of the drive means need not again be shown and described. Moreover, raw feed material is fed into the chamber 12' by an appropriate feed assembly 29' which may be similar to the feed assembly 29 illustrated in FIG. 1. I

As in the embodiment illustrated in FIG. 1, quantities of gas and material can be peripherally vented out of the chamber 12' by the discharge duct 38'. By varying the diameter of the duct 38', the amount of partially ground material and gas discharged per unit time can be varied. In the embodiment illustrated in FIG. 6 the gas and' partially ground material passing through discharge duct 38' are connected to a cyclone separator rather than being directly aspirated back into a jet. As illustrated in FIG. 6, the discharge duct 38' is preferably connected tangentially to the inner wall 102 of the cyclone 100. The cyclone 100 operates in the conventional manner of the well known cyclone separator. In other words, it functions to separate the gas and material. As shown, substantially all of the gas carrying the partially ground material is vented out of the cyclone separator through the duct 106. It will be understood by those skilled in the art that the size of the duct 106 is determined by the size of the cyclone separator 100. Since some material may escape with the gas through duct 106, it may be connected to a bag collector (not shown) or a similar collection device.

The material separated from the gas in the cyclone is aspirated into the gaseous stream being emitted by the nozzle 108 connected to a source of high pressure gas,

not shown. The material is accelerated in the venturi 110 and thus re-injected into the chamber 12 against the rotating anvils.20' in the manner described with respect to the embodiment illustrated in FIGS. 1 and 2.

The operation of the apparatus illustrated in FIGS. 5.

and 6 is more efficient than that of FIG. 1 by reason of the separation of substantially all of the gas from the material. The reason for this is that the energy required for re-injecting the material back into the chamber 12' is applied to the material per se rather than the gas and material. Moreover, the lesser frictional effect of the particles alone on the acceleration means such as the venturi results in higher velocities of the injected material. Still further, the re-injected material is highly concentrated rather than diluted by recycled gas resulting in more interaction of the material as it passes through the venturi 110. It is known that a certain amount of grinding actually occurs in the venturi. The removal of the gas enhances this grinding.

' Since the anvils 20' rotating within the chamber 12' maintain a substantially constant rotative velocity of the gas within the chamber, the particles of material circulated with the gas are subjected to a substantially constant centrifugal force. However, since a considerable'portion of the gas is removed from the mill, there is substantially less gas flowing from the peripheral walls of the chamber 12 to the product outlet 14. As a result, the inward viscous drag of the gas is substantially reduced allowing finer particles to be retained within the chamber 12' for further grinding. This enhances the classifying effect within the chamber 12'.

If desired, the gas separated from the material need not be discharged through duct 106. Instead, it can be re-inserted into the chamber 12' through the duct 112 in amounts controlled by the valve 114. Of course, valve 107 is closed when the gas is fed back into chamber 12'. The enhanced classifying effect is eliminated when the gas is fed back into the chamber through the duct 112. However, the enhanced comminuting effect and acceleration of the particles within the venturi 110 remain.

Another advantage of the apparatus illustrated in FIGS. 5 and 6 is that the size of the chamber 12 can be substantially reduced because it is not longer necessary to have a classification zone large enough to handle the larger quantities of gas circulating at a rotationally inward velocity compatible with the particle size desired. Hence a smaller mill is possible. An advantage of a smaller mill generating the same particle size as a larger mill is that the concentration of material at the periphery of the chamber 12 is greater thereby resulting in less relative internal friction surfaces and greater interaction between particles.

If desired, the cyclone 100 can 'be water cooled by passing water or another coolant between walls 102 and 104. Inlet duct 116 and outlet duct 118 are provided for this purpose.

Referring now to FIGS. 7 and 8, there is shown yet another embodiment of the present invention-The embodiment illustrated in FIGS. 7 and 8 incorporates the principles of the present invention with those disclosed in US. Pat. No. 3,348,779. As shown, the mill'comprises a grinding and classifying chamber 12" of substantially circular cross section formed by the side plates 120 and 122 mounted on the peripheral wall 124. A plurality of nozzles 126 are spaced around the peripheral wall 124 and communicate with the header 128. A pipe connects the header to a supply of gas through which air or steam is forced under pressure into the header 128 and through the nozzles 126. The nozzles 126 are angularly directed so that the jet streams created thereby are tangent to a circle of less diameter than the inner periphery of wall 124.

An outlet duct 14" of sufiicient size to permit the discharge of products together with the circulating gas is provided in the center of side plate 122.

The raw-material to be comminuted is introduced into the chamber 12" by means of the feed assembly 29" which may be similar to the assembly 29 illustrated in FIG. 1. I

As in the embodiment of FIG. 1, the shaft 16" rotatably mounts the frame 18" about whose periphery are spaced the anvils 20".

A discharge duct 38". is tangentially connected to the wall l24'in the manner of duct 38 in 'FIG. 'l.

Discharge duct 38" provides communication for partly ground material and gas to the re-injection and -ac-' celeration assembly 39". The acceleration assembly 39" may be the same as the assembly 39 illustrated in FIG. 2.

In operation, the rotating anvils 20" discharge duct 38" and acceleration assembly 39" function to re-inject partially ground material into the chamber 12' in the manner heretofore described. Thus, the partially ground material is further comminuted by the jet and anvil principles of the present invention. Moreover, material slides along the peripheral wall 124 in the manner described in US Pat. No. 3,348,779 where it is aspirated into the jets issuing from nozzles 126 and further ground in the manner of a jet pulverizer. The ground particles are removed from the'chamber 12" through the product outlet duct 14" in the manner heretofore described and well known in the art.

Referring now to FIG. 9, there is shown another form of comminuting apparatus illustrating how the principles of the present invention may be embodied into a toroidal type of mill.

As shown, the anvils 20" are mounted on the frame 18" for rotation with the chamber 12. The anvils 20" are shaped and mounted in much the same. manner that is illustrated in FIGS. 1 and 2. Moreover,

the drive illustrated in FIG. 4 can be used to rotate the frame 18" and hence the anvils 20".

The chamber 12" is in communication with a straight duct 132 which in turn is connected to a semicircular duct 134. The semicircular duct 134 is in communication with another straight duct 136 which in turn opens into direct communication with the periphery of chamber 12. A product outlet duct 138 is provided in the semicircular duct 134. The classifying effect of these ducts is well known in the art and need not be described in detail.

The product to be ground is introduced into the chamber 12" by means of the feed assembly 29" which functions in the same manner as the assembly 29 in FIG. 1. Thus, raw material is fed from the funnel 30" into the gaseous stream issuing from nozzle 32".

The gaseous stream carries it through venturi 34" which accelerates the material. The feed assembly 29" is adjusted so as to project the raw particles against the rotating anvils 20".

In accordance with the principles of the present invention, partly ground material is discharged through the discharge tube 38" which conducts it to the acceleration means 39". As previously explained, the acceleration means 39" includes a nozzle 40" and venturi 42". The acceleration means 39" is positioned so as to re-inject the material into the chamber 12" so that it impacts against the rotting anvils 20". From the foregoing it should be apparent how the principles explained with respect to the device illustrated in FIG. 1 have been incorporated into a toroidal type of comminuting apparatus such as shown in FIG. 9.

Referring now to FIGS. and 11, there is shown a further embodiment of the present invention. As illustrated, the comminuting apparatus 150 includes a chamber 152 defining a cylindrical housing. Mounted within the chamber 152 by means of the shaft 154 is the frame 156. The shaft 154 is preferably driven by means such as the structure illustrated in FIG. 4. Accordingly, such structure is not illustrated in FIG. 10.

The frame 156 comprises a pair of disc shaped plates 158 and 160 bolted to a cylindrical wall 162, as shown. Each of the plates 158 and 160 is larger in diameter than the wall 162 so that the plates together with the wall define a peripheral channel 164. Mounted within the peripheral channel 164 are a plurality of anvils-166 as shown. The anvils 166 are spaced at equal points about the periphery of the wall 162 within the channel 164. The anvils 166 differ from the anvils used in other apparatus described herein in that they are not L- shaped for reasons to be described hereinafter.

A product outlet duct .168 is provided in the wall below the plate 160 and it functions in the manner known in the art.

Mounted on the outer surface of the plate 158 are a plurality of fan blades 170 which extend radially outward from the shaft 154 to the periphery of the plate 158, as best shown in FIG. 11.

A discharge duct 172 is connected so as to open tangentially into the interior of chamber 152 in the manner of other discharge ducts described herein. The duct 172 receives gas and partially, ground material as it circulates near the wall of chamber 152. The gas and material are conducted by the duct 172 into the cyclone separator 174. As previously described, the cyclone separator separates the gas from the partly ground material by discharging the gas through duct 176. The partly ground material is in turn discharged through the bottom of cyclone separator 174 into the screw conveyor 178 driven by motor 180.

Raw material stored in the hopper 182 is added to the conveyor 178 by means of a rotary pocket feeder 184. Thereafter, the partly ground material and raw material are carried by the conveyor into hopper 186. Hopper 186 communicates directly with hopper 188 which in turn communicates directly with hopper 190. Valve 192 controls the flow of material from hopper 186 to hopper 188 and valve 194 controls the flow of material from hopper 188 to hopper 190. The gas pres-' sure within hoppers 188 and 190 is controlled by the application of high pressure gas through ducts 196, 198 and 200. The flow of gas through duct 200 is controlled by valve 202. Duct 204 and valve 206 provide a means for relieving the pressure within hopper 188.

Hopper 190 is connected to screw conveyor 208 driven by motor 210; Conveyor 208 discharges materi al into nozzle 212 which is connected to a source of high pressure gas. Nozzle 212 accelerates the combined raw and partly ground material into chamber 1 52 against the rotating anvils 166. The re-injection and injection of partly ground and raw material is directed into the chamber in a direction such that it impacts against the surface of anvils 166.

The method of operating the apparatus illustrated in FIGS. 10 and 11 is as follows. At start-up hoppers 186, 188 and 190 are empty. Moreover, all valves are open. Enough raw material is introduced to fill hopper 190. Thereafter, valves 194 and 202 are closed and high pressure gas is applied to nozzle 212. Hence, high pressure gas is also applied to duct 196. At the same time, motor 210 is energized to start conveyor 208 feeding raw material into the nozzle 212. Of course, shaft 154 is rotating the anvils '166 to comminute the material projectedagainst them by the nozzle 212.

Before hopper 190 is empty, valve 192 is opened so that the raw and partly ground material from cyclone 174 collected in hopper 186 empties into hopper 188. As soon as hopper 188 is filled, valves 206 and 192 are closed. Valve 202 is now opened. When the pressure in hopper 188 equals the pressure in hopper 190, valve 194 is open and material in hopper 188 is permitted to fill hopper 190. Thereafter, valve 194 is closed as is valve 202. Valve 206 is opened so that hopper 188 can be returned to atmospheric pressure. Then valve 192 is opened and hopper 188 again refilled from hopper 186.

The hopper-conveyor feed mechanism described herein is for illustrative purposes. The operation of the valves could be either manual or it could be automated. Still further, different forms of feed mechanisms are known in the art and may be used to discharge partly ground and raw material in the nozzle 212, as desired.

In the embodiment illustrated in FIG. 10, the width of the channel 164 is large in respect to the diameter of the nozzle 212 because there is considerable lateral spreading of the material and gas after impacting against the anvils 166 although this will be less direct than if the anvils were stationary. To protect plates 158 and they are coated with a hard, wearresisting material 214 and 216.

The side of chamber 152 nearest to the fan blades is provided with a duct 218 which is connected to a source of relatively low pressure gas. The pressure is only sufficient to ensure flow through the chamber 152 and out the product outlet. The fan blades 170 create a whirling effect on the low pressure gas which mixes with and increases the rate of whirling of gas leaving the channel 164 after impact with the anvil 166.

The apparatus illustrated in FIG. 10 has been found to be particularly adapted for grinding various types of hard materials such as certain metal powders, particularly those that are both hard and fairly friable. Since most materials of this type are not normally ground to as fine a particle size as many other materials, the anvils 166 are located further from the nozzle 212.

Referring now to FIGS. 12 and 13, there is shown a further embodiment of the present invention. The comminuting apparatus 150' is similar to the apparatus illustrated in FIGS. 10 and 11. Accordingly, like structural features are indicated by primed numbers. As illustrated, the comminuting apparatus-150 includes a chamber 152' defining a cylindrical housing. Mounted within the chamber 152 by means of a shaft 154 is the frame 156. The shaft 154' is preferably driven by means such as illustrated in FIG. 4, or the like. 'Accordingly, such structure is not illustrated in FIG. 12.

The frame 156' comprises a pair of disc shaped plates 158' and 160 bolted to a cylindrical wall 162, as shown. Each of the plates 158' and 160 is larger in diameter than the wall 162 so that the plates together with the wall'define a peripheral channel 164. The structure illustrated in FIGS. 12 and 13 differs from what is illustrated in FIGS. and 11 in that there are no anvils mounted on the cylindrical wall 162.

A product outlet duct 168' is provided in the wall below plate 160', and it functions in the manner shown in the art.

Mounted on the outer surface of the plate 158 are a plurality of fan blades 170' which extend radially outward from the shaft 154' to the periphery of the plate 158', as best shown'in FIG. 13.

A discharge duct 172' is connected so as to open tangentially into the interior of chamber 152' in the manner of other discharge ducts described herein. Discharge duct 172 receives gas and partially ground material as it circulates near the wall 152'. The gas and material are conducted by the duct 172 into a cyclone separator (not shown). The gas and material conducted into the cyclone separator may be treated with apparatus similar to what is illustrated in FIG. 10. Accordingly, such apparatus is not shown or described in detail. It should be sufficient to state that the combination of partially ground and raw material is fed into nozzle 212 whichis connected to a source of high pressure gas (not .shown). Nozzle 212 accelerates to combine raw and partly ground material into chamber 152' against the surface of wall 162'.

.The apparatus illustrated in FIGS. 12 and 13 operates in the same manner as the apparatus illustrated in FIGS. 10 and 11, with the exception of the fact that they are no anvils. The apparatus illustrated in FIGS. 12 and 13 is particularly advantageous for grinding highly abrasive materials which would destroy rotating anvils in a relatively short time. It is also advantageous for grinding gummy, sticky, or slightly damp material which would tend to cake up or build up between the anvils .until they are rendered inoperable.

Thus, the apparatus illustrated in FIGS. 12 and 13 is designed to accomplish substantially the same effect as the apparatus of FIG. 10, and other apparatus, but be more efficient when operating with particular types of materials. The advantages of the embodiment illustrated in FIGS. 12 and 13 is that a fresh anvil surface is continuously presented to the discharge of raw material and partly ground material exiting from nozzle 212'. Although the smooth surface defined by wall 162 is not as effective as the rotating anvils previously described, the concept of providing a close spacing between the impact surface and the end of acceleration means 212' or its equivalent without the build-up of a pressure head is still present. Thus, the disadvantages of a stationary anvil are avoided.

The conceptof a rotating smooth surface without sequentially defined anvils can also be applied to the embodiment illustrated in FIG. 7. Thus, the present invention contemplates the re-injection of partly ground material against the peripheral surface of the disc 18" rather than against the anvils 20".

As previously described with respect to the apparatus illustrated in FIGS. 5 and 6, the gas bearing the material can be separated from the material by means of a cyclone and the material can thereafter be re-injected. Those skilled in the art should recognize that this concept of separation of the gas from the material prior to re-injection of the material itself can be readily adapted for use with all of the embodiments illustrated in the present invention.

Moreover, the apparatus illustrated in FIG. 10 wherein original feed material and recirculated material are introduced into the high pressure gas, and both directed against an anvil, illustrates a concept which can be applied with respect to the other embodiments of the present invention.

The present invention may be embodied in other specific forms without departing from the spirit or 'essential attributes thereof and, accordingly, reference should be made to the appended claims, rather than to the foregoing specification as indicating the scope of the invention.

I claim: 1. In a comminuting apparatus of the jet and anvi type, said apparatus including an anvil rotatably mounted within a housing having an outer curvilinear surface, means for the introduction of material to be ground into said apparatus, discharge means on the outer curvilinear surface of the apparatus for the discharge of partially ground material circulating in the apparatus, gaseous fluid injector means for accelerating said partially ground material and injecting it into high velocity'impact with said rotating anvil, and outlet means for discharging fully ground material, said outlet means being inward from said discharge means for partially ground material.

2. In a comminuting apparatus of the jet and anvil type in accordance with claim 1 wherein said material discharge meansincludes means to-divert at least a potion of the gaseous fluid carrying said partly ground' material away from said partly ground material.

3. In a comminuting apparatus of the jet and anvil type in accordance with claim 2 wherein said diverting means is'a cyclone separator.

4. In a comminuting apparatus of the jet and anvil type in accordance with claim. 2 including means to return the diverted portion of the gaseous fluid back into said chamber.

5. In a comminuting apparatus of the jet and anvil type, said apparatus including an endless'casing of the curvilinear type,'a disc rotatably mounted within said casing, said disc having a multiplicity of vanes to cause the rapid circulation of gaseous fluid within said casing, discharge means on the outer curvilinear portion of the casing for the discharge of coarser fractions of material circulating within the casing, gaseous fluid injector means for accelerating said coarser materials and in-,

jecting it into high velocity impact with said rotating vanes, and outlet means spaced inwardly of the outer curvilinear portion of the casing for the discharge of finished materials.

6. In a comminuting apparatus of the jet'and anvil type in accordance with claim 5, a plurality of jet nozzles spaced about the periphery of said casing, said jet nozzles being connected to a source of high pressure gaseous fluid, said jet nozzles being positioned to define a jet grinder for further grinding of partially ground material received from said vanes.

7. In a comminuting apparatus of the jet and anvil type in accordance with claim wherein said casing defines a torroidal grinding chamber.

8. In a comminuting apparatus of the jet and anvil type in accordance with claim 1 including means to inject material to be ground into said discharge means, whereby said material to be ground and partially ground material are simultaneously injected into high velocity impact with said rotating anvil.

9. In a comminuting apparatus of the jet and anvil type, said apparatus including an anvil rotatably mounted within a housing having an outer curvilinear surface, means for the introduction of feed material to be ground into said apparatus, discharge means on the outer curvilinear surface of the apparatus for the discharge of coarser fractions of material circulating in the apparatus, gaseous fluid injector means for accelerating said coarser materials and injecting it into high velocity impact with said rotating anvil, and outlet means for discharging fully ground material from said apparatus, said outlet means being positioned inward from said discharge means for coarser material.

10. In a comminuting apparatus of the jet and anvil type in accordance with claim 9 wherein said discharge means on the outer curvilinear surface of the apparatus includes means for diverting at least a portion of the gaseous fluid carrying coarser material away from said coarser material.

11. A method of finely comminuting raw material comprising the steps of partially grinding raw. material by injecting said raw material into a housing against an anvil rotating in a chamber having an outer curvilinear surface, discharging circulating partially ground material from the chamber at the outer curvilinear surface of the chamber, and re-injecting the material into the chamber against a rotating anvil using gaseous fluid injector means for accelerating said partially ground material and injecting it at high velocity impact with said rotating anvil, and removing fully ground material from said chamber at an outlet inward from said discharge at the outer curvilinear surface of the chamber.

12. A method in accordance with claim 11 including the step of separating a portion of the gas carrying said partly ground material from material and gas removed from said housing.

13. In a comminuting apparatus of the jet and anvil type, said apparatus including a plurality of anvils rotatably mounted in a housing having an outer curvilinear surface, means for the introduction of material to be ground into said housing, discharge means on the discharge means for piartially ground materia s.

14. In a comminu ng apparatus 1n accor ance with claim 13 wherein said material discharge means includes means to divert at least a portion of the gas carrying said partly ground material away from said partly ground material.

15. A method of finely comminuting raw material comprising the steps of partially grinding raw material by injecting said raw material into a housing against a plurality of anvils rotating in a chamber having an outer curvilinear surface, discharging circulating partially ground material from the chamber at the outer curvilinear surface of the chamber, and re-injecting the material into the chamber against rotating anvils using gaseous fluid injector means for accelerating said partly ground material and injecting it at high velocity impact with said rotating anvils, and removing fully ground material from said chamber at an outlet inward from said discharge at the outer curvilinear surface of the chamber.

16. A method in accordance with'claim 15 including the step of separating a portion of the gas carrying said partly ground material from said material and gas removed from said housing.

17. In a comminuting apparatus of the jet and anvil type, said apparatus including an endless casing of the curvilinear type, a plurality of anvils mounted within said casing, raw material feed means feeding raw material into said casing for comminution, gaseous fluid acceleration means directed into said casing so as to accelerate partially comminuted material to be further comminuted against said rotating anvils, and communication means extending between an outer curvilinear surface of said casing and said acceleration means for conducting partly comminuted material from said casing to said acceleration means for re-injection into said casing against said rotating anvils, means supporting a plurality of radially extending fan blades positioned laterally of said anvils, and means forinjecting a source of low pressure gas into said chamber adjacent said rotating fan blades, whereby said fan blades create a gas flow to mix with said material to increase the gas flow of material exiting from said casing, and outlet means for discharging finished product, said outlet means being spaced inwardly of the outer curvilinear surface of said casing. 

2. In a comminuting apparatus of the jet and anvil type in accordance with claim 1 wherein said material discharge means includes means to divert at least a potion of the gaseous fluid carrying said partly ground material away from said partly ground material.
 3. In a comminuting apparatus of the jet and anvil type in accordance with claim 2 wherein said diverting means is a cyclone separator.
 4. In a comminuting apparatus of the jet and anvil type in accordance with claim 2 including means to return the diverted portion of the gaseous fluid back into said chamber.
 5. In a comminuting apparatus of the jet and anvil type, said apparatus including an endless casing of the curvilinear type, a disc rotatably mounted within said casing, said disc having a multiplicity of vanes to cause the rapid circulation of gaseous fluid within said casing, discharge means on the outer curvilinear portion of the casing for the discharge of coarser fractions of material circulating within the casing, gaseous fluid injector means for accelerating said coarser materials and injecting it into high velocity impact with said rotating vanes, and outlet means spaced inwardly of the outer curvilinear portion of the casing for the discharge of finished materials.
 6. In a comminuting apparatus of the jet and anvil type in accordance with claim 5, a plurality of jet nozzles spaced about the periphery of said casing, said jet nozzles being connected to a source of high pressure gaseous fluid, said jet nozzles being positioned to define a jet grinder for further grinding of partially ground material received from said vanes.
 7. In a comminuting apparatus of the jet and anvil type in accordance with claim 5 wherein said casing defines a torroidal grinding chamber.
 8. In a comminuting apparatus of the jet and anvil type in accordance with claim 1 including means to inject material to be ground into said discharge means, whereby said material to be ground and partially ground material are simultaneously injected into high velocity impact with said rotating anvil.
 9. In a comminuting apparatus of the jet and anvil type, said apparatus including an anvil rotatably mounted within a housing having an outer curvilinear surface, means for the introduction of feed material to be ground into said apparatus, discharge means on the outer curvilinear surface of the apparatus for the discharge of coarser fractions of material circulating in the apparatus, gaseous fluid injector means for accelerating said coarser materials and injecting it into high velocity impact with said rotating anvil, and outlet means for discharging fully ground material from said apparatus, said outlet means being positioned inward from said discharge means for coarser material.
 10. In a comminuting apparatus of the jet and anvil type in accordance with claim 9 wherein said discharge means on the outer curvilinear surface of the apparatus includes means for diverting at least a portion of the gaseous fluid carrying coarser material away from said coarser material.
 11. A method of Finely comminuting raw material comprising the steps of partially grinding raw material by injecting said raw material into a housing against an anvil rotating in a chamber having an outer curvilinear surface, discharging circulating partially ground material from the chamber at the outer curvilinear surface of the chamber, and re-injecting the material into the chamber against a rotating anvil using gaseous fluid injector means for accelerating said partially ground material and injecting it at high velocity impact with said rotating anvil, and removing fully ground material from said chamber at an outlet inward from said discharge at the outer curvilinear surface of the chamber.
 12. A method in accordance with claim 11 including the step of separating a portion of the gas carrying said partly ground material from material and gas removed from said housing.
 13. In a comminuting apparatus of the jet and anvil type, said apparatus including a plurality of anvils rotatably mounted in a housing having an outer curvilinear surface, means for the introduction of material to be ground into said housing, discharge means on the outer curvilinear surface of the housing for the discharge of partially ground material circulating in the apparatus, gaseous fluid injector means for accelerating said partially ground material and injecting it into high velocity impact with said rotating anvils, and outlet means for discharging fully ground material from said housing, said outlet means being inward from said discharge means for partially ground materials.
 14. In a comminuting apparatus in accordance with claim 13 wherein said material discharge means includes means to divert at least a portion of the gas carrying said partly ground material away from said partly ground material.
 15. A method of finely comminuting raw material comprising the steps of partially grinding raw material by injecting said raw material into a housing against a plurality of anvils rotating in a chamber having an outer curvilinear surface, discharging circulating partially ground material from the chamber at the outer curvilinear surface of the chamber, and re-injecting the material into the chamber against rotating anvils using gaseous fluid injector means for accelerating said partly ground material and injecting it at high velocity impact with said rotating anvils, and removing fully ground material from said chamber at an outlet inward from said discharge at the outer curvilinear surface of the chamber.
 16. A method in accordance with claim 15 including the step of separating a portion of the gas carrying said partly ground material from said material and gas removed from said housing.
 17. In a comminuting apparatus of the jet and anvil type, said apparatus including an endless casing of the curvilinear type, a plurality of anvils mounted within said casing, raw material feed means feeding raw material into said casing for comminution, gaseous fluid acceleration means directed into said casing so as to accelerate partially comminuted material to be further comminuted against said rotating anvils, and communication means extending between an outer curvilinear surface of said casing and said acceleration means for conducting partly comminuted material from said casing to said acceleration means for re-injection into said casing against said rotating anvils, means supporting a plurality of radially extending fan blades positioned laterally of said anvils, and means for injecting a source of low pressure gas into said chamber adjacent said rotating fan blades, whereby said fan blades create a gas flow to mix with said material to increase the gas flow of material exiting from said casing, and outlet means for discharging finished product, said outlet means being spaced inwardly of the outer curvilinear surface of said casing. 